+AC_SUBST(SUBARCHTYPE)
+
+[
+#if test "x$ARCHTYPE" = "xx86" -a "x$host_cpu" != "xi386" -a "x$host_cpu" != "xi486" -a "x$host_cpu" != "xi586"; then
+#For now, using lock; addl compatibility mode even for i686, because the
+#Pentium III is seen as a i686, but lacks mfence instruction.
+#Only using fence for x86_64.
+if test "x$ARCHTYPE" = "xx86" -a "x$host_cpu" != "xi386" -a "x$host_cpu" != "xi486" -a "x$host_cpu" != "xi586" -a "x$host_cpu" != "xi686"; then
+]
+ AC_DEFINE([CONFIG_RCU_HAVE_FENCE], [1])
+[
+fi
+]
+
+AC_MSG_CHECKING([sys_futex()])
+AC_TRY_COMPILE(
+[
+#include <sys/syscall.h>
+],
+[
+#ifndef __NR_futex
+#error "futexes not available"
+#endif
+],
+[
+ AC_MSG_RESULT([yes])
+ AC_DEFINE([CONFIG_RCU_HAVE_FUTEX], [1])
+ compat_futex_test=0
+]
+,
+[
+ AC_MSG_RESULT([no])
+ compat_futex_test=1
+]
+)
+
+AM_CONDITIONAL([COMPAT_FUTEX], [ test "x$compat_futex_test" = "x1" ])
+
+AM_CONDITIONAL([COMPAT_ARCH], [test "x$SUBARCHTYPE" = xx86compat ])
+
+[
+if test "x$SUBARCHTYPE" = xx86compat; then
+]
+ AC_DEFINE([CONFIG_RCU_COMPAT_ARCH], [1])
+[
+fi
+]
+
+AC_ARG_ENABLE([smp-support], [ --disable-smp-support Disable SMP support. Warning: only use this
+ on uniprocessor systems. [[default=enabled]]], [def_smp_support=$enableval], [def_smp_support="yes"])
+
+[
+if test "$def_smp_support" = "no"; then
+ echo "SMP support disabled."
+else
+]
+ AC_DEFINE([CONFIG_RCU_SMP], [1])
+[
+ echo "SMP support enabled."
+fi
+]
+
+# From the sched_setaffinity(2)'s man page:
+# ~~~~
+# The CPU affinity system calls were introduced in Linux kernel 2.5.8.
+# The library interfaces were introduced in glibc 2.3. Initially, the
+# glibc interfaces included a cpusetsize argument. In glibc 2.3.3,
+# the cpuset size argument was removed, but this argument was
+# restored in glibc 2.3.4.
+# ~~~~
+
+# In addition to that, some vendors ported the system call to 2.4
+# kernels.
+
+# Furthermore, when the function first appeared, the MASK argument was
+# an unsigned long pointer, while later it was made into a cpu_set_t
+# pointer. Systems that have the cpu_set_t version also should have
+# the CPU_ZERO, CPU_SET, etc. macros.